Catheters are introduced into the cardiovascular system for various diagnostic and therapeutic reasons. Catheters are often introduced into the cardiovascular system through introduction sheaths that provide a pre-determined conduit from the access site to the treatment site and facilitate vascular access of new catheters as well as the exchange of catheters within the vasculature. Such catheters and introducer sheaths are used in both the arterial, higher pressure, circulation and the venous, lower pressure, circulation. Introducer sheaths suitable for guiding devices through the vasculature and into the right or left atrium of the heart are prime examples of such vascular access.
The introducer sheaths and catheters used for these purposes are generally primed with saline and purged of any air prior to being inserted into the patient's cardiovascular system through a percutaneous or open surgical access to an artery or vein. The purpose of purging air from a catheter or introducer sheath is to prevent that air from inadvertently being forced, under a pressure drop generated within the catheter or sheath, out the distal end of the catheter and into the patient's circulatory system.
The act of inserting a therapeutic or diagnostic catheter through an introducer sheath can cause air or other gas to be introduced into the central lumen of the introducer sheath. Such air can migrate distally into the patient's cardiovascular system under certain circumstances, especially when the distal end of the introducer sheath is located within the venous side of the cardiovascular system or in the left atrium of the heart. In certain pathological and physiological states, relatively low pressures can exist within the venous side of the heart with a pressure gradient existing between the right and left atrium. Such gradients in the presence of a Patent Foramen Ovale (PFO), a not uncommon congenital cardiac condition, can easily result in air emboli traversing from the right heart to the left heart during right heart interventional procedures. In addition, these relatively low pressures can exist for a non-trivial portion of the cardiac cycle resulting in the potential for a negative pressure gradient between the room pressure, which in a clean room, catheterization lab, or surgical suite is generally slightly elevated, and the distal end of the introduction sheath. There is a potential for any gas or air entrained into the proximal end of the introduction sheath to migrate out the distal end of the introduction sheath and into the patient's cardiovascular system where it could cause an air embolism. During a portion of the cardiac cycle, pressures within the left atrium can approach very low values and can even go negative relative to room pressure.
The clinical ramifications of an air embolism range from no noticeable effect to cerebrovascular stroke or cardiac ischemia, either of which could have mild to severe outcomes and could even result in patient death. Air can also be entrained out the distal end of the sheath by surface tension forces between the catheter and the air. This surface tension can cause the air to adhere to the catheter while it is advanced out the distal end of the sheath. Thus, any air that inadvertently enters the sheath or catheter system is at risk for introduction to the patient, an event with potentially catastrophic consequences such as cerebrovascular embolism, coronary embolism, and the like. Air embolism is clearly an issue especially with catheters directed toward the cerebrovasculature or the coronary circulation, but also with catheters or sheaths directed anywhere within the circulatory system of the mammalian patient.
New devices and methods are needed to more efficiently remove gas that inadvertently migrates into a catheter or sheath so that it is prevented from being routed into the patient's cardiovascular system. The need has been heightened by recent Medicare regulations that restrict or deny reimbursement for certain hospital acquired conditions including air embolism.